Wu Ona, Østergaard Leif, Koroshetz Walter J, Schwamm Lee H, O'Donnell Joanie, Schaefer Pamela W, Rosen Bruce R, Weisskoff Robert M, Sorensen A Gregory
Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology/Harvard Medical School, Boston, 02129, USA.
Magn Reson Med. 2003 Oct;50(4):856-64. doi: 10.1002/mrm.10610.
A common technique for calculating cerebral blood flow (CBF) and mean transit time (MTT) is to track a bolus of contrast agent using perfusion-weighted MRI (PWI) and to deconvolve the change in concentration with an arterial input function (AIF) using singular value decomposition (SVD). This method has been shown to often overestimate the volume of tissue that infarcts and in cases of severe vasculopathy to produce CBF maps that are inconsistent with clinical presentation. This study examines the effects of tracer arrival time differences between tissue and a user-selected global AIF on flow estimates. CBF and MTT were calculated in both numerically simulated and clinically acquired PWI data where the AIF and tissue signals were shifted backward and forward in time with respect to one another. Results show that when the AIF leads the tissue, CBF is underestimated independent of extent of delay, but dependent on MTT. When the AIF lags the tissue, flow may be over- or underestimated depending on MTT and extent of timing differences. These conditions may occur in practice due to the application of a user-selected AIF that is not the "true AIF" and therefore caution must be taken in interpreting CBF and MTT estimates.
一种计算脑血流量（CBF）和平均通过时间（MTT）的常用技术是利用灌注加权磁共振成像（PWI）追踪一团对比剂，并使用奇异值分解（SVD）将浓度变化与动脉输入函数（AIF）进行去卷积。已表明该方法常常高估梗死组织的体积，并且在严重血管病变的情况下会产生与临床表现不一致的CBF图。本研究考察了组织与用户选择的全局AIF之间示踪剂到达时间差异对血流估计的影响。在数值模拟和临床采集的PWI数据中计算CBF和MTT，其中AIF和组织信号在时间上相对于彼此向前和向后移动。结果表明，当AIF领先于组织时，无论延迟程度如何，CBF都会被低估，但取决于MTT。当AIF落后于组织时，血流可能会根据MTT和时间差异程度被高估或低估。由于应用的是用户选择的而非“真实AIF”的AIF，这些情况在实际中可能会出现，因此在解释CBF和MTT估计值时必须谨慎。
